Adapter for a cable-television network

ABSTRACT

An adapter includes a passive branch circuit configured to communicate a first cable television (CATV) signal between an input port and a passive port, an active branch circuit configured to receive a second CATV signal from the input port, and a sensor configured to detect a low-power condition in the active branch circuit. The active branch circuit is configured to terminate the second CATV signal in response to the sensor detecting the low-power condition, and the active branch circuit is configured to communicate the second CATV signal from to one or more active ports when the active branch circuit does not terminate the second CATV signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/145,355, filed on May 3, 2016, which is a continuation of U.S. patentapplication Ser. No. 12/175,366 filed on Jul. 17, 2008, now U.S. Pat.No. 9,363,469. Each of these priority applications is incorporatedherein by reference in its entirety.

FIELD

This invention relates to transmission and reception of radio- orhigh-frequency signals over cable networks, such as cable television(CATV) networks. More particularly, the present invention relates to anew and improved passive-active terminal adapter and method whichdelivers high-frequency signals to subscriber devices in a way thatautomatically maintains high signal integrity by minimizing returnlosses in the event of an inoperative or abnormally operative conditionof the terminal adapter.

BACKGROUND OF THE INVENTION

Cable television (CATV) service providers offer television, data,telephone and other entertainment and useful services to subscribers atthe subscriber's premises. The typical medium for delivering theseservices is a cable network which is formed by a relatively large numberof high-frequency, electrical signal-conducting coaxial conductors orcables, all of which are linked together to distribute thehigh-frequency signals over a wide geographic area to substantialnumbers of geographically separated subscribers. The high-frequencysignals are delivered to television sets, computers, telephones andother subscriber devices, and those subscriber devices convert theinformation carried by the high-frequency signals into the services thatthe subscriber desires.

Because of the extensive nature of the cable network, the signalsreceived at the subscriber premises are reduced in strength compared tothe strength of the transmitted signals. The amount of signal strengthreduction depends on the length of the pathway through the cable networkwhich the signals pass before arriving at the subscriber premises. Forthis reason, it is typical to provide an amplifier at the subscriberpremises to increase or amplify the strength of the signals receivedfrom the cable network before delivering the signals to the subscriberdevices.

Some types of subscriber devices, such as television sets, deliverbetter performance in response to receiving amplified signals. Othertypes of subscriber devices may require non-amplified or passive signalsfor proper functionality. For example, “life-line” telephone serviceoperates on the basis of passive signals received at the customerpremises, because the functionality of such telephone service cannotdepend on the proper functionality of an amplifier or other activesignal conditioner in the signal path. A failed or inoperative amplifieror other active device in the signal path could completely terminatetelephone communications, which could be dangerous in emergencysituations.

Passive-active terminal adapters have been developed to provide bothpassive and amplified signals at the subscriber premises for the twodifferent types of subscriber devices which operate from passive andamplified (active) signals. Such passive-active terminal adaptersinclude a splitter which essentially divides or branches the incoming or“downstream” signals from the cable network into passive downstreamsignals and active downstream signals. The passive downstream signalsare conducted through a passive branch of the terminal adapter withoutamplification or modification and applied to those subscriber deviceswhich require passive signals for operation, such as, for example, avoice modem for a telephone set. The active downstream signals areconducted to an amplifier or active signal conditioner of an activebranch of the terminal adapter. The amplifier or signal conditioneramplifies the strength of the signals or modifies some characteristic ofthe signals before the amplified or conditioned signals are delivered toone or more subscriber devices. The amplified or conditioned signalsbenefit the performance and functionality of the subscriber devices,such as a television sets and computers.

The high-frequency signals conducted through the cable network aresusceptible to distortion from a number of sources. It is for thisreason that coaxial cables are widely used to shield the high-frequencysignals from degrading influences of the ambient environment. Onerequirement for maintaining high-quality signal conduction in a coaxialcable is properly terminating the coaxial cable. An improper terminationcauses reflections of the incident signals back into the transmissionpath. The reflections cause degradation of the desired incident signalsreceived by the subscriber. The degradations are exemplified byamplitude ripple, group delay ripple, latency, and other similar effectswhich distort or reduce the incident signals. The signal reflectionscause the subscriber to experience a degraded quality of service, or insome cases the level of degradation may be so severe as to prevent thesubscriber from receiving meaningful service.

SUMMARY OF THE INVENTION

An adapter for a cable-television (CATV) network is disclosed. Theadapter includes an input port configured to connect to a CATV networkso as to receive downstream signals therefrom and to provide upstreamsignals thereto, and a signal splitter coupled to the input port, thesignal splitter having a first terminal and a second terminal. Thesignal splitter is configured to communicate the downstream signals tothe first terminal and the second terminal. The adapter also includes anactive port configured to connect to a first subscriber device, and anactive branch circuit coupled to the first terminal of the signalsplitter and the active port, the active branch circuit being configuredto be coupled to a power supply. The active branch circuit includes atleast one powered device configured to be powered by the power supply, asignal termination having an impedance configured to match an impedanceof a cable of the CATV network, and a switch configured to switchbetween an operative state and a termination state. When the switch isin the operative state, the switch is configured to direct thedownstream signals from first terminal of the signal splitter toward theactive port. When the switch is in the termination state, the switch isconfigured to direct the downstream signals from the first terminal ofthe signal splitter toward the signal termination. The adapter furtherincludes a sensor coupled to the switch. The sensor is configured todetermine that the active branch circuit is operating in a low-powercondition or a fault condition, and wherein the sensor is configured tocause the switch to move from the operative state to the terminationstate in response to the sensor determining that the active branchcircuit is in the low-power condition or the fault condition. Theadapter also includes a passive port configured to connect to a secondsubscriber device, and a passive branch circuit coupled to the secondterminal of the signal splitter and the passive port. The passive branchcircuit is configured to communicate the downstream signals from thesecond terminal of the signal splitter to the passive port.

An adapter is disclosed. The adapter includes a passive branch circuitconfigured to communicate a first cable television (CATV) signal betweenan input port and a passive port, an active branch circuit configured toreceive a second CATV signal from the input port, and a sensorconfigured to detect a low-power condition in the active branch circuit.The active branch circuit is configured to terminate the second CATVsignal in response to the sensor detecting the low-power condition, andthe active branch circuit is configured to communicate the second CATVsignal from to one or more active ports when the active branch circuitdoes not terminate the second CATV signal.

An adapter is disclosed. The adapter includes an input port configuredto receive downstream signals from a cable television (CATV) network,and to provide upstream signals thereto, a passive port configured toconnect to a first subscriber device and to receive first upstreamsignals therefrom, an active port configured to connect to a secondsubscriber device and to receive second upstream signals therefrom, apassive branch circuit configured to communicate the downstream signalsand the first upstream signals between the input port and the passiveport, and an active branch circuit comprising a switch and at least onepowered component. The active branch circuit is configured tocommunicate the downstream signals and the second upstream signalsbetween the input port and the active port when the switch is in a firststate. The active branch circuit is configured to terminate thedownstream signals when the switch is in a second state. The adapteralso includes a sensor coupled to the switch, the sensor beingconfigured to detect that the active branch circuit is in a low-powercondition, and signal the switch to be in the second state in responseto detecting that the active branch circuit is in the low-powercondition.

Other aspects of the invention, and a more complete appreciation of thepresent invention, as well as the manner in which the present inventionachieves the above described and other improvements, can be obtained byreference to the following detailed description of a presently preferredembodiment taken in connection with the accompanying drawings, which arebriefly summarized below, and by reference to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a passive-active terminal adapter whichincorporates the present invention, shown connected to a cable networkand subscriber devices located at a subscriber's premises, which areillustrated in block diagram form.

FIG. 2 is a block diagram of components within the passive-activeterminal adapter shown in FIG. 1.

FIG. 3 is a more detailed block and schematic diagram of the componentsshown in FIG. 2.

FIGS. 4A, 4B and 4C are graphs of signals which illustrate a normaloperating condition, and over-current abnormally operative condition andan under-current abnormally operative condition, respectively, of asensor shown in FIG. 3.

DETAILED DESCRIPTION

A passive-active terminal adapter 1 0 which incorporates the presentinvention is shown in FIG. 1. The terminal adapter 10 includes a housing12 which encloses active and passive internal electronic circuitcomponents (shown in FIGS. 2 and 3). A mounting flange 14 surrounds thehousing 12, and holes 16 in the flange 14 allow attachment of theterminal adapter 1 0 to a support structure at a subscriber's premises18. Downstream high-frequency signals are supplied from a headend (notshown) of a cable network 20, such as a cable television (CATV) network,and the downstream signals are delivered to the terminal adapter 1 0 atan input/output cable port 22 connected to the cable network 20.

The passive and active internal electronic circuit components within thehousing 12, shown in FIG. 2, include a conventional directional coupleror signal splitter 24 which separates the input downstream signals fromthe cable network 20 at the cable port 22 into a passive branchdownstream signals 26, which are conducted through a passive branchcircuit 28, and into an active branch downstream signals 30, which areconducted through an active branch circuit 32.

The passive branch downstream signals 26 are delivered from a passiveport 34 to those subscriber devices which respond to passive signals,such as a voice modem 36 connected to a telephone set 38, or an embeddedmultimedia terminal adapter (EMTA, not shown) which is located at thesubscriber premises 18 (FIG. 1). The telephone set 38 and the voicemodem 36, or the EMTA, generate upstream signals which are delivered tothe passive port 34 and are conducted through the passive branch circuit28 and the splitter 24 and are applied to the cable port 22 andconducted over the cable network 20 to the headend (not shown) of thecable network.

The active branch signals 30 are supplied to a relay switch 40 which,when in its normal operative position shown in FIGS. 2 and 3, conductsthe active branch downstream signals 30 to active branch circuitry 41 ofthe terminal adapter 10. The active branch circuitry 41 includes ananalog downstream filter 42, an analog upstream filter 43 and at leastone active signal conditioner, such as a linear amplifier 44. The analogdownstream filter 42 filters the active branch downstream signals 30 andsupplies the filtered downstream signals to the amplifier 44. Theamplifier 44 amplifies or conditions the downstream active branchsignals 30 and supplies them to at least one, but preferably, aplurality of active ports 46, 48, 50 and 52. The active ports 46, 48, 50and 52 deliver the amplified or conditioned active branch downstreamsignals 30 to subscriber devices located at the subscriber premises 18(FIG. 1), such as television sets (TV) and/or data modems 54, 56, 58 and60. Other data processing devices, such as computers, are connected tothe data modems.

The equipment at the subscriber's premises typically generates upstreamsignals which are supplied to the terminal adapter 10 for subsequentdelivery to the headend (not shown) of the cable network 20. Theupstream signals may be generated by the subscriber devices connected toany of the active ports 46, 48, 50 and 52. For example, one or more ofthe TV sets 54, 56, 58 and 60 may have conventional set top boxes (notshown) associated with them to allow the subscriber/viewer to makeprogramming and viewing selections. Of course, any computers (not shown)connected to the data modems 54, 56, 58 and 60 typically communicateupstream signals.

The upstream signals from the devices at the subscriber's premises maybe amplified by a reverse amplifier or reverse signal conditioner(neither shown) of the terminal adapter 10, before those amplified orconditioned upstream signals are delivered to the relay switch 40, thesplitter 24, the cable port 22 and the cable network 20. Amplifying orconditioning the upstream signals is optional, since the upstreamsignals from subscriber devices are often passively transmitted withoutamplification through the active branch circuit 32 to the cable network20. If a reverse amplifier or reverse signal conditioner (neither shown)is employed in a terminal adapter, such a device is connected in serieswith the analog upstream filter 43 to create an amplifying effect.

Electrical power for the active branch circuitry 41 and other componentsof the terminal adapter 10 is supplied from a conventional DC powersupply 62 connected to a dedicated power input port 64. Alternatively,electrical power can be supplied through a conventional power inserter(also shown at 54) that is connected to the port 46. The power inserterallows relatively low voltage DC power to be conducted through the sameport that also conducts the high-frequency signals, which in thesituation shown in FIGS. 2 and 3, is the port 46. A power-signal divider65 separates the high-frequency signals from the low voltage DC powerand conducts the high-frequency signals to the active branch circuitry41 and conducts the low voltage DC power to the same point that power issupplied from the dedicated port 64. Thus, regardless of whetherelectrical power is supplied through either one of the ports 46 or 64,the DC power operates the active components of the terminal adapter 10.Use of a conventional power inserter connected to one of the ports, e.g.port 30 46, eliminates the need for a separate dedicated power supplyport 64, or provides an alternative port through which electrical powercan also be applied. The power supply 62 or the power supplied from theport 46 is typically derived from a conventional wall outlet (not shown)within the subscriber premises 18.

The ports 22, 34, 46, 48, 50, 52 and 64 are each preferably formed by aconventional female coaxial cable connector (shown in FIG. 1) which ismechanically connected to the housing 12 (FIG. 1) and which iselectrically connected to certain internal components (FIGS. 2 and 3) ofthe terminal adapter 1 0. Using a female coaxial cable connector for theports 22, 34, 46, 48, 50, 52 and 64 facilitates connecting coaxialcables (not shown) to the terminal adapter 10, by mechanicallyconnecting the corresponding mating male coaxial cable connector (notshown) on the coaxial cable to the female coaxial cable connectorsforming the ports 22, 34, 48, 50, 52, and 64.

The present invention automatically minimizes or reduces return loss bypreventing excessive signal reflections which affect downstream signalspassing through the passive branch circuit 28, in the event that thecomponents of the terminal adapter, principally those of the activecircuitry 41, become inoperative or abnormally operative. An inoperativeor abnormally operative condition changes the impedance of the activecircuitry 41, causing downstream signals to reflect back from the activecircuitry 41 into the splitter 24, where those reflected signalsinterfere with and degrade the characteristics of the passive branchsignals 26.

The proclivity for high-frequency signals to reflect is related to theimpedance characteristics of the termination of the conductor whichconducts those signals and to the frequency of those signals. For thisreason, coaxial cables are typically terminated by connecting aterminating impedance between the signal-carrying center conductor andthe surrounding reference plane shielding which has a terminatingimpedance value equal to a characteristic impedance between thesignal-carrying conductor and the reference plane shielding. When theactive circuitry 41 becomes inoperative or abnormally operative, theimpedance of the active circuitry 41 enters an unintended andunanticipated state and causes significantly increased signalreflection, which leads to significantly increased return loss. Returnloss refers to the amount of degradation of incident signals caused byreflected signals. An increase in the amount of the reflected signalsincreases the degradation of the incident signals, thereby causing aloss in the quality or fidelity of the incident signals. A greateramount of return loss equates to more downstream signal reflection.Minimizing the return loss maximizes the quality and fidelity of thedownstream signals.

The active circuitry 41 enters an unanticipated impedance state, whichalters the impedance of the active circuitry 41, if the terminal adapter10 becomes inoperative as a result of losing its supply of appliedelectrical power or losing an adequate supply of applied electricalpower. Under such circumstances the voltage from the power supplydiminishes. A power loss of this nature may result from a failed powersupply 62, or a disconnection or breakage in the conductor whichsupplies the electrical power from the power supply to one of the powerinput port 64 or 46.

The active circuitry also enters an unanticipated impedance state, whichalters the impedance of the active circuitry 41, if a component of theterminal adapter fails and causes it (principally the amplifier 44) toconsume an excessive amount of current, as would occur if a componentfailure caused a short circuit, or if a component of the terminaladapter fails and causes it (principally the amplifier 44) to consume adiminished amount of current, as would occur if a component failurecaused an open circuit. The current drawn by the active circuitry 41increases if the amplifier 44 enters a short-circuit condition, and thecurrent drawn by the active circuitry 41 decreases if the amplifier 44enters an open-circuit condition. Even if some other circuit componentof the active circuitry 41 becomes defective, that other circuitcomponent has the potential of adversely affecting the amplifier 44, andmay cause the amplifier 44 to consume more or less current than it wouldnormally supply.

A sensor 66, shown in FIG. 2, responds to changes in the voltage of thepower supplied and/or to changes in the current consumed by the terminaladapter 10. Under inoperative or abnormally operative conditions, thesensor 66 sends a control signal 68 to a switch driver 70. The switchdriver 70 responds to the control signal 68 by causing the relay switch40 to disconnect the active circuitry 41 from the active branch circuit32 and to substitute a predetermined termination impedance 72 as theimpedance for the active branch circuit 32.

The impedance value and characteristics of the termination impedance 72are selected to minimize the signal reflections into the splitter 24 andthe cable network 20, thereby minimizing the return loss and preservingthe characteristics of the passive branch signals 26 conducted in thepassive branch circuit 28. The impedance value of the terminationimpedance 72 is preferably selected to match the inherent characteristicimpedance of the coaxial cables which form the cable network 20.Matching the termination impedance to the characteristic impedance ofthe coaxial cables minimizes signal reflections, for reasons which arewell known. Since the typical coaxial cable has an inherent impedance of75 ohms, the termination impedance has an impedance value of 75 ohms.Although the termination impedance 72 is shown and described as a singleimpedance element, it could also formed by a combination of real andreactive impedance elements.

By preserving the characteristic of the passive signals 26, the veryimportant or essential subscriber devices, such as a “life-line”telephone set 38, will continue to operate without a substantialdecrease in performance. Maintaining the telephone set 38 in afunctional state is important in assuring the subscriber access toeffective communication in emergency and urgent situations, as well asgenerally permitting high-fidelity voice communications undercircumstances where an abnormally operative condition of the activecircuitry 41 would prevent high-fidelity voice communications.

Of course when the active circuitry 41 is disconnected, active signalsare not conducted to the subscriber devices 54, 56, 58 and 60.High-quality signals would not be available to these subscriber devicesin any event because the inoperative or abnormally operative conditionof the terminal adapter. The subscriber devices connected to the activeports 46, 48, 50 and 52 are considered expendable in operation in orderto preserve the more critical functionality of “life-line” passivetelephone communications through the telephone set 38.

Under normal operative conditions, the relay switch 40 is held in itsnormal operating position shown in FIGS. 2 and 3. Under inoperative orabnormally operative conditions, the switch driver 70 does not supplyenergy to hold the relay switch 40 in the normal operating positionshown in FIGS. 2 and 3, but instead the relay switch 40 naturally movesunder the influence of its own internal mechanical bias to thealternative position (not shown) where the termination impedance 72 isconnected in substitution for the active circuitry 41 in the activebranch circuit 32.

When normal power delivery resumes and when power is normally supplied,the switch driver 70 will move the relay switch 40 to the normaloperating position shown in FIGS. 2 and 3. However, it is unlikely thata component failure or degradation will be temporary, so it is unlikelythat the terminal adapter will resume normal operation after anexcessive amount of current is consumed due to a failed or degradedcomponent or after a minimal amount of current is consumed due to afailed or degraded component.

An indicator 74 is attached to the switch driver 70. Whenever the switchdriver 70 holds the relay switch 40 in the normal position shown, theindicator 74 delivers an indication of normal functionality, such as agreen light. Whenever the switch driver 70 allows the relay switch 40 toconnect the termination impedance 72 in substitution for the activecircuitry 41, the indicator 74 delivers a different type of indication,such as a red light, which indicates an inoperative or abnormallyoperative condition. Of course, if there is a lack of power to theterminal adapter 1 0, the indicator 74 will not deliver any type ofindication. The lack of any indication itself indicates a loss of power.The indicator 74 delivers the indication through a view window 75 in thehousing 12 (FIG. 1).

More details concerning the sensor 66 and its interaction with the othercomponents of the terminal adapter 10 are shown in FIG. 3. Downstreamsignals from the cable network 20 are divided by the splitter 24 intothe downstream passive branch signals 26 and the downstream activebranch signals 30. The downstream active branch signals 30 are suppliedto the relay switch 40, which is shown in FIG. 3 in 25 its normaloperating position conducting the downstream active branch signals 30 tothe active circuitry 41. After filtering in the analog downstream filter42, the downstream active branch signals 30 are applied to the amplifier44, where the magnitude of those signals is amplified, modified orconditioned and thereafter supplied to an upstream/downstream filter 76.The filter 76 supplies the filtered active downstream signals to theactive ports 46, 48, 50 and 52, and from there to subscriber devicessuch as the TV sets and data modems 54, 56, 58 and 60. Upstream signalsgenerated by the subscriber devices 54-60 are supplied through theactive ports 46-52 through the upstream/downstream filter 76 and theanalog upstream filter 43, and conducted back through the relay switch40 while in its normal operating position to the splitter 24 and intothe cable network 20 through the cable port 22. The filters 42, 43 and76 are conventional. The filters 42 and 43 form a conventional diplexer.

The DC electrical power supplied at the input ports 46 and 64 istypically from a conventional low-voltage transformer power supply thatis connected to a conventional AC electrical power outlet. The inputelectrical power is supplied to node A, and is typically at an upperlevel of about 16 volts, for example. The input electrical power isapplied to a first voltage regulator 77, which reduces the upper levelvoltage at node A to an intermediate voltage level at node B, such as 9volts, for example. The first voltage regulator 77 supplies the majorityof the electrical power to the components of the terminal adapter 10from node B, although power for the indicator 74 is supplied from nodeA. The electrical current delivered from the first voltage regulator 77to node B flows through a current sense resistor 78.

The intermediate voltage at node B is applied to a second voltageregulator 79, which further reduces the voltage to a low level at nodeC, such as 5 volts, for example. The second voltage regulator 79regulates the low level output voltage at node C to a constant level,and applies that low-voltage level to a storage capacitor 80 whichfurther acts to maintain a constant voltage at node C. The voltage atnode C is supplied to a resistor divider network formed by resistors 81,82 and 83. The resistors 81, 82 and 83 are connected in series betweennode C and a voltage reference 84 of the terminal adapter. Because thevoltage at node C is relatively constant, the voltage 85 at the junctionbetween resistors 81 and 82, and a voltage 86 at the junction betweenresistors 82 and 83, are likewise relatively constant. The values of theresistors 81, 82 and 83 are selected to establish the voltage 85 at avalue which is indicative of an over-current condition of the terminaladapter (principally exemplified by a short-circuit condition of theamplifier 44 in the active circuitry 41), and to establish the voltage86 at a value which is indicative of an under-current condition of theterminal adapter (principally exemplified by an open-circuit conditionof the amplifier 44 in the active circuitry 41).

The voltages 85 and 86, the voltages at nodes A and C and the voltageacross the current sense resistor 78 are applied to operationalamplifiers (op amps) 87, 88, 89 and 90 to detect the inoperative andabnormally operative conditions.

To detect a low-voltage input power condition, the voltage at node A iscompared with the voltage at node C, at negative and positive inputterminals of the op amp 87, which functions as a comparator. Because thevoltage at node C will remain stable at its low level for a short timeafter the supply voltage decreases at node A, due to the action of thevoltage regulators 77 and 79 and the storage capacitor 80, comparing thevoltage at node A with the voltage at node C provides an indication whenthe input voltage diminishes to a level where the functionality of theterminal adapter 10 is not reliable.

Under normal conditions, because the voltage at node A is greater thanthe voltage at node C, the op amp comparator 87 supplies the controlsignal 68 at a logic low level. The low-level control signal 68 isapplied to a first NPN transistor 94 of the switch driver 70. Thelow-level signal biases the NPN transistor 94 into a nonconductivestate, thereby causing current to flow through a resistor 96 and to thebase of an NPN transistor 98. The transistor 98 is biased into a fullyconductive state, causing current to flow through a resistor 100. Theconductive transistor 98 and the current flow through the resistor 100bias a PNP transistor 102 into a fully conductive state. The conductivetransistor 102 conducts current through a relay solenoid 104 to hold therelay switch 40 in the normal operating position shown in FIG. 3. Onlyenergizing the relay solenoid 104 will move the relay switch 40 to thenormal operating position shown in FIG. 3. When the relay solenoid 104is not energized, the relay switch 40 will revert to the alternativeposition where the relay switch 40 conducts the downstream active branchsignals 30 through the termination impedance 72.

If the voltage of the input power begins to decline to a point which islower than the voltage at node C, the voltage comparator 87 supplies alogic high level control signal 68. The high-level control signal 68biases the NPN transistor 94 into conductivity, which in turn biases theNPN transistor 98 into a nonconductive state. The nonconductivetransistor 98 biases on the NPN transistor 102 into a nonconductivestate, thereby terminating the current flow through the relay solenoid104. With the relay solenoid 104 no longer energized or activated, therelay switch 40 moves to the alternative position from that shown inFIG. 3, thereby connecting the termination impedance 72 in place of theactive circuitry 41. Thus, under low input voltage conditions, thevoltage comparator 87 causes the relay switch 40 to connect thetermination impedance 72 in place of the active circuitry 41. Signalreflections to the passive branch circuit 28 (FIG. 2) are minimized,thereby minimizing the return loss which would otherwise adverselyinfluence the passive branch signals 26.

Under normal operating conditions, the current consumed by the terminaladapter 10 remains within a normal range of current levels. The currentconsumed by the terminal adapter 10 is conducted through the currentsensing resistor 78. The voltage across the current sensing resistor 78,caused by the amount of current it conducts, represents the amount ofcurrent conducted by the terminal adapter 10. Positive and negativeinput terminals of a current sensing op amp 88 are connected across thecurrent sensing resistor 78. A voltage signal 108 is developed by the opamp 88 which relates to the amount of current conducted through thesensing resistor 78. Thus, the voltage signal 108 from the op amp 88represents the amount of current conducted by the terminal adapter 10.

The voltage signal 108 from the op amp 88 is compared to the voltagesignals 85 and 86 by the comparators 89 and 90, respectively, torecognize normal operating conditions, an inoperative condition orabnormally operative conditions. The inoperative or abnormal operativecondition may be caused by a malfunction of the amplifier 44, a failureof one of the biasing components of the amplifier 44, or a failure ofone of the other passive components within the filters 42, 43, and 76which adversely affect the bias and current consumption of the amplifier44 itself, for example.

Normal operating conditions are illustrated in FIG. 4A. The voltagelevel of the current-related signal 108 remains less than the voltage 85and greater than the voltage 86. Under these conditions, the currentrelated voltage signal 108 indicates that the terminal adapter 10 isdrawing current within its normal range of current ranges between theupper limit represented by the voltage 85 and the lower limitrepresented by the voltage 86. Because the current-related voltagesignal 108 is less than the voltage 85, the comparator 89 supplies a lowlevel output control signal 68. Similarly, because the current relatedsignal 108 is greater than the voltage 86, the comparator 90 supplies alow level output control signal 68. Of course under these circumstances,with adequate power being supplied to the terminal adapter 10, thevoltage comparator 87 also supplies a low level output control signal68. Consequently, the transistor 94 is biased into a nonconductivestate, while the transistors 98 and 102 are biased into conductivestates, which cause current to flow through the relay solenoid 104 tohold the relay switch 40 in the normal operating position shown in FIG.3.

The inoperative or abnormally operative condition caused by the terminaladapter 10 consuming more than the normal upper limit of the range ofcurrent is shown graphically in FIG. 4B. Under conditions of excessivecurrent consumption, the voltage across the sensing resistor 78increases, and that signal is amplified by the op amp 88. The voltagelevel of the signal 108 exceeds the voltage 85. Under suchcircumstances, the voltage signal 108 to the positive input terminal ofthe op amp comparator 89 exceeds the level of the voltage 85 applied tothe negative input terminal of the op amp comparator 89, causing thecomparator 89 to supply a high level logic signal as the control signal68. The high logic signal 68 causes the transistor 94 to conduct, whichin turn biases the transistor 98 into a nonconductive state therebycausing the transistor 102 to become nonconductive. The relay solenoid104 ceases conducting current, allowing the mechanical bias on the relayswitch 40 to move the switch to the alternative position from that shownin FIG. 3. The alternative position of the relay switch 40 connects thetermination impedance 72 to the splitter 24 in place of the activecircuitry 41. Thus, in over-current or short-circuit conditions of 25the terminal adapter 10, represented by high current consumption sensedat the sensing resistor 78, an inoperative or abnormally operativecondition is indicated, and the termination impedance 72 is connected tothereby minimize signal reflections and return loss.

During the over-current condition described in the preceding paragraph,the current-related voltage signal 108 exceeds the voltage 86, causingthe op amp comparator 90 to supply a low-level signal. Similarly, thevoltage sensing op amp 87 also supplies a low-level signal because thelevel of voltage supplied to the terminal adapter 10 remains normal.Consequently, the over-current sensing op amp 89 controls the high levelcontrol signal 68 supplied to the switch driver 70.

The inoperative or abnormally operative condition of the terminaladapter 10 consuming less than the lower limit of the normal range ofcurrent is shown graphically in FIG. 4C. Under conditions of minimalcurrent consumption, the voltage across the sensing resistor 78decreases. The diminished value of the signal across the sensingresistor 78 is amplified by the op amp 88. The voltage level of thesignal 108 is less than the voltage 86. Under such circumstances, thevoltage signal 108 to the negative input terminal of the op ampcomparator 90 is less than the level of the voltage 86 applied to thepositive input terminal of the op amp comparator 90, causing thecomparator 90 to supply a high-level logic signal as the control signal68. The high logic signal 68 causes the transistor 94 to becomeconductive, which in turn biases the transistor 98 into a nonconductivestate thereby causing the transistor 102 to become nonconductive. Therelay solenoid 104 ceases conducting current, allowing the mechanicalbias on the relay switch 40 to move the switch to the alternativeposition from that shown in FIG. 3. The alternative position of therelay switch 40 connects the termination impedance 72 to the splitter 24in place of the active circuitry 41. Thus, in under-current oropen-circuit conditions of the terminal adapter 10, represented by lowcurrent consumption sensed at the sensing resistor 78, an inoperative orabnormally operative condition is indicated, and the terminationimpedance 72 is connected as the active branch 32 to thereby minimizesignal reflections and return loss.

During the under-current condition described in the preceding paragraph,the current-related voltage signal 108 is less than the voltage 85,causing the op amp comparator 89 to supply a low-level signal.Similarly, the voltage sensing op amp 87 also supplies a low-levelsignal because the level of voltage supplied to the terminal adapter 10remains normal. Consequently, the under-current sensing op amp 90controls high level control signal 68 supplied to the switch driver 70.

Under normal operating conditions, when the transistor 102 is conductiveand the relay solenoid 104 is energized, an LED 110 also receives powerfrom the conductive transistor 102. The LED 110 preferably emits a colorof light, such as green light, indicating normal functionality of theterminal adapter 10. The LED 110 is therefore illuminated to indicatenormal functionality whenever the relay solenoid 104 is energized by theconductive transistor 102. The conductive transistor 102 also provides abias signal to a NPN transistor 112, causing the transistor 112 toconduct current through the resistor 114 from the voltage at node A. Theconductive transistor 112 diverts current flow from a second LED 116,preventing energization and light emission from the LED 116. However, inthe event of any of the abnormally operative conditions discussed above,the transistor 102 becomes nonconductive, causing the transistor 112 tobecome nonconductive and allowing current flow through the resistor 114to the LED 116. The LED 116 is energized and emits light of a color toindicate an abnormally operative condition, such as red light. The lightfrom the LEDs 110 and 116 is conducted through a view window 75 formedin the housing 12 of the terminal adapter 10, as shown in FIG. 1.

Thus, the light emitted from the LED 110 constitutes a visual signalindicating a normal operative condition, during which the upstream anddownstream active branch signals 30 are conducted through the activecircuitry 41. The light emitted from the LED 116 constitutes a visualsignal indicating an abnormally operative condition, during which theupstream and downstream active branch signals are conducted through thetermination impedance 72. Emission of no light from the view window 75formed in the housing 12 (FIG. 1) is in itself an indication of aninoperative condition, typically caused by a lack of power supplied tothe terminal adapter 10. Under such circumstances, the upstream anddownstream active branch signals are conducted through the terminationimpedance 72.

Minimizing the return loss by connecting the termination impedance 72 asthe active circuit branch 32 (FIG. 2) maintains the reliability andfidelity of the passive downstream signals conducted by the splitter 24to passive signal-responsive subscriber equipment such as the voicemodem 36 and the telephone 38. The reliability of communications whenusing such passive equipment is enhanced under conditions where aninoperative or abnormally operative condition may occur in the activecircuitry 41 of the active branch circuit 32. Connecting the terminationimpedance 72 enhances the capability of communication through theessential passive subscriber equipment, which can be very importantunder urgent and emergency circumstances.

The significance of these and other improvements and advantages willbecome apparent upon gaining a full appreciation of the ramificationsand improvements of the present invention. A preferred embodiment of theinvention and many of its improvements have been described with a degreeof particularity. The detail of the description is of preferred examplesof implementing the invention. The detail of the description is notnecessarily intended to limit the scope of the invention. The scope ofthe invention is defined by the following claims.

What is claimed is:
 1. An adapter for a cable-television (CATV) network,the adapter comprising: an input port configured to connect to a CATVnetwork so as to receive downstream signals therefrom and to provideupstream signals thereto; a signal splitter coupled to the input port,the signal splitter having a first terminal and a second terminal,wherein the signal splitter is configured to communicate the downstreamsignals to the first terminal and the second terminal; an active portconfigured to connect to a first subscriber device; an active branchcircuit coupled to the first terminal of the signal splitter and theactive port, the active branch circuit being configured to be coupled toa power supply, and the active branch circuit comprising: at least onepowered device configured to be powered by the power supply; a signaltermination having an impedance configured to match an impedance of acable of the CATV network; a switch configured to switch between anoperative state and a termination state, wherein: when the switch is inthe operative state, the switch is configured to direct the downstreamsignals from first terminal of the signal splitter toward the activeport, and when the switch is in the termination state, the switch isconfigured to direct the downstream signals from the first terminal ofthe signal splitter toward the signal termination; a sensor coupled tothe switch, wherein the sensor is configured to determine that theactive branch circuit is operating in a low-power condition or a faultcondition, and wherein the sensor is configured to cause the switch tomove from the operative state to the termination state in response tothe sensor determining that the active branch circuit is in thelow-power condition or the fault condition; a passive port configured toconnect to a second subscriber device; and a passive branch circuitcoupled to the second terminal of the signal splitter and the passiveport, wherein the passive branch circuit is configured to communicatethe downstream signals from the second terminal of the signal splitterto the passive port.
 2. The adapter of claim 1, wherein the sensor isconfigured to detect the low-power condition in response to apower-input voltage of the power supply being below a lower voltagethreshold.
 3. The adapter of claim 2, wherein: the sensor comprises atleast one voltage regulator configured to couple to the power supply;and the sensor is configured to measure the lower voltage thresholddownstream from the at least one voltage regulator.
 4. The adapter ofclaim 1, wherein the sensor is configured to detect the low-powercondition in response to a current consumption in the active branchcircuit being below a lower threshold, and to detect the fault conditionin response to the current consumption in the active branch circuitbeing above an upper threshold.
 5. The adapter of claim 4, wherein thesensor comprises: a first voltage regulator configured to couple to thepower supply; and a second voltage regulator coupled to the firstvoltage regulator, downstream therefrom, such that the first voltageregulator is in series between the power supply and the second voltageregulator, wherein the sensor is configured to determine the currentconsumption between the first and second voltage regulators, and whereinthe sensor is configured to determine the upper and lower thresholdsbased on voltages measured downstream from the second voltage regulator.6. An adapter, comprising: a passive branch circuit configured tocommunicate a first cable television (CATV) signal between an input portand a passive port; an active branch circuit configured to receive asecond CATV signal from the input port; and a sensor configured todetect a low-power condition in the active branch circuit, wherein theactive branch circuit is configured to terminate the second CATV signalin response to the sensor detecting the low-power condition, and whereinthe active branch circuit is configured to communicate the second CATVsignal from to one or more active ports when the active branch circuitdoes not terminate the second CATV signal.
 7. The adapter of claim 6,wherein the active branch circuit comprises a switch that is configuredto change state in response to the sensor detecting that the activebranch circuit is operating in the low-power condition.
 8. The adapterof claim 7, wherein: the switch in a first state is configured to directthe second CATV signal from the input port toward the one or more activeports; the switch in a second state is configured to direct the secondCATV signal from the input port toward a signal termination, the signaltermination having an impedance configured to match an impedance of acable to which the input port is configured to connect; and when theswitch is not energized, the switch is in the second state.
 9. Theadapter of claim 6, wherein the active branch circuit comprises at leastone powered component, and the passive branch circuit does not includeany powered components.
 10. The adapter of claim 6, wherein the sensoris configured to detect the low-power condition by determining that apower-input voltage to at least a portion of the active branch circuitis lower than a threshold voltage.
 11. The adapter of claim 10, whereinthe sensor comprises: one or more voltage regulators coupled to a powersupply configured to supply power to the active branch circuit, whereinthe power-input voltage is measured between the one or more voltageregulators and the power supply, and wherein the threshold voltage ismeasured downstream from at least one of the one or more voltageregulators; and a comparator configured to compare the power-inputvoltage with the threshold voltage.
 12. The adapter of claim 6, whereinthe sensor is configured to detect the low-power condition bydetermining that a current consumption in at least a portion of theactive branch circuit is lower than a lower threshold.
 13. The adapterof claim 6, wherein the sensor is configured to detect a fault conditionin the active branch circuit by determining that a current consumptionin at least a portion of the active branch circuit is greater than anupper threshold, and wherein the active branch circuit is configured toterminate the second CATV signal in response to the sensor detecting thefault condition.
 14. The adapter of claim 13, wherein the sensorcomprises: a first voltage regulator coupled to a power supplyconfigured to supply power to at least a portion of the active branchcircuit; a second voltage regulator coupled to the first voltageregulator; and a comparator configured to generate an outputproportional to a current between the first and second voltageregulators; wherein the sensor is configured to detect the faultcondition in response to the output of the comparator being greater thanan upper voltage threshold measured downstream from the second voltageregulator, and wherein the sensor is configured to detect the low-powercondition in response to the output of the comparator being less than alower voltage threshold measured downstream from the second voltageregulator, the lower voltage threshold being less than the upper voltagethreshold.
 15. An adapter, comprising: an input port configured toreceive downstream signals from a cable television (CATV) network, andto provide upstream signals thereto; a passive port configured toconnect to a first subscriber device and to receive first upstreamsignals therefrom; an active port configured to connect to a secondsubscriber device and to receive second upstream signals therefrom; apassive branch circuit configured to communicate the downstream signalsand the first upstream signals between the input port and the passiveport; an active branch circuit comprising a switch and at least onepowered component, wherein: the active branch circuit is configured tocommunicate the downstream signals and the second upstream signalsbetween the input port and the active port when the switch is in a firststate; and the active branch circuit is configured to terminate thedownstream signals when the switch is in a second state; and a sensorcoupled to the switch, the sensor being configured to: detect that theactive branch circuit is in a low-power condition; and signal the switchto be in the second state in response to detecting that the activebranch circuit is in the low-power condition.
 16. The adapter of claim15, wherein the sensor is further configured to measure a currentconsumption of at least a portion of the active branch circuit, avoltage input level of at least a portion of the active circuit, orboth, and to detect that the active branch circuit is operating in thelow-power condition based at least in part on the current consumption,the voltage input level, or both.
 17. The adapter of claim 16, whereinthe sensor is configured to determine that the low-power conditionexists when: the voltage input to at least a portion of the activebranch circuit is below a lower voltage threshold; or the currentconsumption is below a lower current threshold.
 18. The adapter of claim17, wherein the sensor comprises at least one voltage regulatorconfigured to connect to a power supply, wherein the sensor isconfigured to: measure the voltage input between the at least onevoltage regulator and the power supply; measure the lower voltagethreshold downstream from the at least one voltage regulator; anddetermine the lower current threshold based on at least one voltagemeasurement downstream from the at least one voltage regulator.
 19. Theadapter of claim 15, wherein the at least one powered component of theactive branch circuit comprises an amplifier to amplify the downstreamsignals received via the input port.
 20. The adapter of claim 15,wherein the passive branch circuit is configured to communicate signalsfrom the input port to the passive port when the switch is in the firststate and when the switch is in the second state.
 21. The adapter ofclaim 15, wherein, when the switch is energized, the switch isconfigured to be in the first state, and when the switch is notenergized, the switch is configured to be in the second state.